1. Field of the Invention
The present invention relates to a cleaning apparatus for removing substances from a surface and in particular to a blade cleaning device for use in an image forming device such as an electrostatic copying machine to remove residual toner particles and unwanted substances from a photosensitive surface.
2. Discussion of the Related Art
In an electrophotographic process, such as xerography, an optical device oscillates a light pattern along a charged photosensitive surface to form a latent image corresponding to an electrical or optical input. The resulting pattern of charged and discharged areas on the surface forms an electrostatic latent image corresponding to the original image. Developing devices of the electrostatic copying machine develop the latent image using yellow, magenta, cyan, and/or black developing toners. The developing toners are composed of electrostatically attractable powder and are attracted to the latent image areas formed on the charged photosensitive surface. The developed image is then transferred to a predetermined image medium, e.g., paper, to produce a reproduction and a permanent record of the original image.
When the developed image is transferred onto a paper, a majority of developing toner is transferred to the paper. However, some residual toner remains on the charged photosensitive surface because of the relatively high electrostatic and/or mechanical forces between the electrostatically attracted toner and the charged photosensitive surface. Further, other unwanted substances, e.g., paper fibers, Kaolin, debris, etc., are attracted to the charged photosensitive surface and remain on the charged photosensitive surface. Because the residual toner and unwanted substances left on the charged photosensitive surface will degrade the quality of the reproduced image, it is essential to remove the residual toner and unwanted substances from the charged photosensitive surface during each image development process.
Blade cleaning is a highly desirable method for removing the residual toner and unwanted substances because it is simple and inexpensive compared to the various known fiber or magnetic brush cleaners A blade cleaning device comprises a relatively thin elastomeric cleaning blade member which is provided and supported adjacent to the charged photosensitive surface and is transverse to the charged photosensitive surface relative to the direction of the relative movement. The cleaning blade has a blade edge chiselling or wiping the residual toner from the charged photosensitive surface during the doctoring mode or wiping mode, respectively. Thus, the residual toner and unwanted substances are removed from the surface prior to developing another latent image on the charged photosensitive surface. The removed residual toner and unwanted substances which accumulate adjacent to the cleaning blade are transported away from the cleaning blade area by a toner transport arrangement or by gravitational force.
However, the blade cleaning method has certain deficiencies caused by the frictional and adhesional forces between the cleaning blade and the charged photosensitive surface. The frictional and adhesional forces cause a wearing away of the cleaning blade edge and damages the charged photosensitive surface.
Further, the cleaning blade is subject to unpredictable failures due to improper and excessive tuck characteristics. Normally, the blade cleaning edge or tip is tucked slightly when the cleaning blade edge or tip is chiselling or wiping the toner from the charged photosensitive surface and slides on the toner particles and lubricants to maintain a sealing contact required for cleaning. During removal of the residual toner and unwanted substances, the cleaning blade may flatten toner that passes underneath the blade edge and cause compaction of toner on the charged photosensitive surface. The impact from carried beads of toner remaining on the charged photosensitive surface subsequent to development may damage the cleaning blade due to sudden localized increase in frictional and adhesional forces between the cleaning blade and the charged photosensitive surface. Such sudden increase in frictional and adhesional forces cause the phenomenon of excessive tucking, i.e., blade foldover, where the blade cleaning edge becomes tucked underneath the blade. As a result, the cleaning blade looses the frictional and adhesional sealing relationship required for blade cleaning. Such problems ultimately require removal and replacement of the cleaning blade because the blade is torn or is so distorted in shape that the cleaning blade no longer functions to remove the residual toner and unwanted substances.
U.S. Pat. No. 4,937,633 to Ewing, assigned to Xerox Corporation, discloses a cleaning blade defect sensing arrangement. An elastomeric cleaning blade supported in cleaning relationship with an imaging surface of an electrophotographic device is provided for removal of residual toner on the surface and has a cleaning edge having predetermined and detectable characteristics. An electrical signal is applied to the cleaning edge and variations in the electrical characteristics are monitored. Changes in the electrical characteristics of the cleaning blade edge will be highly indicative of a cleaning blade failure, or impending failure. A signal based on the variation in electrical characteristics may be produced to create a warning indication or cause a corrective response to occur.
U.S. Pat. No. 4,942,387 to Thomas discloses a device for determining cutting tool wear and breakage. The device has a vibration sensor, such as an accelerometer, which is mounted on or near the tool. An output signal from the sensor is computed into functions of AC and DC power of the vibration signals. The functions are then compared and if the relationship between the AC and DC power changes beyond selected limits, an alarm is sounded or flashed.
U.S. Pat. No. 4,894,644 to Thomas discloses a method and device for detecting gradual wear or breakage of a machine tool which occurs over a period of time by sensing high frequency vibrations produced at a cutting tool/workpiece interface during a machining process. High frequency vibrations are converted to a unipolar vibration signal which is processed to produce a tracking signal and tracks the minimum value of the vibration signal. The vibration signal is related to the effective cutting energy and it decreases due to gradual tool wear or breakage. The tracking minimum signal is compared to a predetermined threshold level to detect excessive wear or breakage of the tool and is provided with an alarm.
U.S. Pat. No. 4,744,242 to Anderson et al. discloses a method for monitoring cutting tool wear during a machining operation. The vibration of an end mill is sensed by either microphones or accelerometers. A time domain signal is produced by these sensors which is converted into a near-real time frequency spectrum. A certain frequency band in the spectrum is directly related to the end mill vibration and certain frequencies in the band will change in amplitude corresponding to certain types of end mill wear. When any of the amplitudes in the band exceed a certain threshold limit, the machine control unit may cause operations to stop, or a monitor may continuously communicate tool wear data to a front end processor which may then issue commands to a machine control unit in response to the tool wear data.
None of the above U.S. patents discloses a cleaning blade having a piezoelectric sensor for generating an electrical signal which indicates the condition of the cleaning blade. Further, none of the above U.S. patents discloses a feedback loop to control the pressure loading of the cleaning blade for the purpose of extending the usable life-span of the blade.